1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device and, more particularly, to a method of manufacturing a semiconductor device, which performs deposition of a barrier metal (e.g., a tungsten nitride (WN) layer) in a fine contact hole having high aspect ratio by an atomic layer deposition process.
2. Description of Related Art
Generally, with the high integration of semiconductor devices, the size of a source/drain and a line width of a gate electrode of a MOS transistor and a line width of metal layer are reduced. In particular, when the line width of the metal layer is reduced, the aspect ratio of a contact hole or a via hole is increased. Accordingly, a conventional physical vapor deposition (PVD) process has a limitation in filling the contact hole or via hole with a tungsten layer. Recently, to solve this problem, a new method of forming a metal layer was developed whereby a contact hole or via hole is filled with a tungsten layer using a chemical vapor deposition (CVD) process and the tungsten layer remains only in the contact hole or via hole by using a chemical mechanical polishing (CMP) process. The tungsten layer is planarized and an aluminum layer is formed on the tungsten layer on the contact hole or via hole. Such process is called a plug process.
In a contact hole having an exposed silicon substrate or a poly silicon layer, a Ti/TiN layer is generally deposited in the contact hole to prevent damage of a bottom face of the contact hole by a fluorine element of the WF6 gas. The WF6 gas is injected into a reaction chamber to deposit the tungsten layer after the formation of the contact hole, and in order to form a stable Ti silicide. In case of the via hole, a Ti/TiN layer or a TiN layer is formed in the via hole after the formation of the via hole. This is conducted for the enhancement of function and bonding characteristic of a barrier metal. As for a material for forming the barrier metal, TiW by a sputtering process, Ti/TiN by the sputtering process, TiN by CVD process or WN by the sputtering process are mainly used. The barrier metal is used because the tungsten layer has poor contact characteristics with a silicon substrate or an oxide layer and is well-grown on a specific layer. A film quality of the barrier metal has a great influence on the film quality of the tungsten layer in an initial nucleation stage and therefore on the whole tungsten layer. The barrier layer serves to prevent damage of a semiconductor device due to the intrusion of a fluorine element of WF6 gas, which is used in the deposition of the tungsten layer, into the semiconductor device.
In the prior art, Ti/TiN layers are sputtered to form a barrier metal for large sized contact or via holes. Ionized Metal Plasma (IMP)-Ti/CVD-TiN layers are used as the barrier metal for small sized contact or via holes.
In the method of forming Ti/TiN layers using the sputtering process, an overhang phenomenon of the Ti/TiN layers 13 and 15 occurs at upper corner portions A of the contact hole 12 of an insulating layer 11 of a semiconductor substrate 10, as shown in FIG. 1. This is attributable to defective step coverage. Also, at lower corner portions of the contact hole 12, a volcano defect may be caused upon deposition of the tungsten layer (not shown) for filling the contact hole 12 because the Ti layer 13 is easily exposed. Since the step coverage of the Ti/TiN layers 13 and 15 is bad, the tungsten layer does not completely fill the contact hole so that a void can occur in the contact hole 12. As a result, this method is not well suited for a micro semiconductor device of 0.18 μm or less.
In the method using IMP-Ti/CVD-TiN layers as a barrier metal, the Ti layer 23 causes a degradation of the bonding properties with the insulating layer 11 because the step coverage at the sidewall C of the contact hole 12 of the insulating layer 11 of the semiconductor substrate 10 is poor.
Also, a TiN layer 25 is deposited on the Ti layer 23 by CVD process and is then plasma-processed. The TiN layer 25 is normally plasma-processed at an outside portion D of the contact hole 12 or at a bottom portion E of the contact hole 12, but cannot be normally plasma-processed along the sidewall F of the contact hole 12 because of the direct motion of the plasma spray. Thus, the Ti/TiN layers 23 and 25 do not completely perform a function as a barrier metal when the tungsten layer fills the contact hole by subsequent CVD process. As a result, the TiN layer 25 at the sidewall F has a defective surface and contains many impurities because of lateral damage caused by the fluorine element. This may cause numerous problems such as an increase in the resistance of the metal thin film, a degradation of the physical properties of the barrier metal layer, an interference of the growth of the tungsten layer (not shown) to fill the contact hole 12, and so forth. This may also cause serious manufacturing problems for micro semiconductor devices of 0.13 μm or less.
In the above-described manufacturing methods, the semiconductor device is moved to separate manufacturing equipment after the deposition of the barrier metal. As such, a vacuum state of the semiconductor substrate may be broken, thus generating a contaminant or natural oxide layer between the barrier metal and the tungsten layer. This may result in a defect in the contact resistance characteristics.
In consideration of the problems associated with the prior art, although it has excellent barrier characteristics, a tungsten nitride (WN) layer as a metal barrier is hardly used at present because of the structural limitations associated with the deposition method using the sputtering process. Thus, it has been required an improvement of deposition method of the tungsten nitride layer.